Polyesters such as poly(alkylene terephthalates) are well known commercially available polymers. They have valuable characteristics including strength, toughness, high gloss and solvent resistance. Polyesters are commercially prepared by the reaction of diols with functional derivatives of dicarboxylic acids, diacid halides or esters. Further, the above-described polyesters may be fabricated into articles by a number of well known techniques including injection and roto molding and extrusion.
In recent years, macrocyclic polyester oligomers have been developed and desired since they have unique properties which make them attractive as matrices for polymer composites. The desired properties stem from the fact that macrocyclic polyester oligomers exhibit low viscosities when compared to those of corresponding polymers. Such low viscosities allow them to easily impregnate dense fibrous preforms.
As a result of their properties, and particularly their low viscosities, it has been of increasing interest to utilize macrocyclic polyester oligomers as precursors for branched and linear polyesters. This is true because macrocyclic polyester oligomers may first be employed to fill a preform, and subsequently polymerized to high molecular weight polyesters displaying the above-mentioned properties. Notwithstanding, it is often difficult to polymerize macrocyclic polyester oligomers due to impurities which may be present and their decreased ability to polymerize after prolonged heating. It is of increasing interest, therefore, to make polyesters by a method which results in improved polymerization of molten macrocyclic polyester oligomers. Additionally, it is particularly desirable to obtain such results when using titanium comprising catalysts since such catalysts are generally preferred when polymerizing macrocyclic polyester oligomers.